1. Field of the Invention
This invention relates to new "drywall" compositions and methods for making the same that are useful in the manufacture of wallboard for covering walls and ceilings in construction applications. More particularly, this invention is directed to a novel wallboard composition comprising a unique combination of synthetic binders selected for their ability to establish a strengthened permanent bond in the final dry state, in combination with an expanded mineral such as Perlite which largely reduces the amount of gypsum present in the wallboard product from what has been required by previous gypsum wallboard formulations. This reduction in the amount of gypsum present in the wallboard formulation in turn reduces the weight of the wallboard structure while maintaining its strength. Moreover, the synthetic binders uniquely cross-link with the expanded mineral to form a much stronger bond between the constituent components of the wallboard core material than that which has been available in previously utilized or known wallboard products. In a preferred embodiment, the lightweight, strengthened wallboard of the present invention also comprises a covering veneer that is applied to the top ply of the face paper to provide increased strength, moisture resistance, and fire retardency, and the back paper top ply is treated to provide increased flexural strength. Additionally, this invention relates to the unique manufacturing process to produce the wallboard composition of the present invention in order to create a lightweight, strengthened, moisture resistant, and fire retardant wallboard used to cover walls and ceilings in construction applications. Still further, this invention relates to the apparatus for manufacturing the wallboard composition of the present invention, including a method and apparatus for economically converting a standard gypsum wallboard manufacturing facility into a facility for manufacturing wallboard of the present invention.
2. Description of the Background
Conventional gypsum drywall has been utilized for approximately the past fifty years in the construction industry with gypsum comprising the primary core ingredient. The manufacture of gypsum drywall is presently an expensive, complex, difficult, and tightly controlled manufacturing process. The gypsum wallboard manufacturing process today entails several elaborate steps with significant environmental concerns, both internally and externally, regarding the product itself and the manufacture thereof. An increasingly shortened supply of domestic gypsum rock remains available today, which has necessitated the development and usage of synthetic gypsum as a substitute. However, the production of synthetic gypsum requires an extremely complex synthetic gypsum production facility. Such facilities include FGD (flu gas desulferization) gypsum production plants which are required by the nature of the manufacturing process to be located next to power plant facilities. These power plants utilize high sulfur coal, which is predominate in the Eastern United States, to generate power. The waste produced by these power plants is classified and desulferized into synthetic gypsum. This synthetic gypsum is then calcined and used as a substitute for natural gypsum for use in the wallboard manufacturing process. Given the significant risk of detrimental long-term health effects of a waste slag and coal product, the processing and use of such synthetic gypsum has also fueled environmental concerns. It is an object of the present invention to provide a new and distinctly different environmentally safe class of wallboard for use in the construction industry that utilizes environmentally friendly synthetic adhesives.
The continuously depleting supply of gypsum coupled with the rising demand for wallboard products has caused the price of gypsum and gypsum-based products to rise substantially over recent years. In the field of gypsum wallboard composition, relatively low prices of materials have kept the core of gypsum wallboard unchanged for the better part of the 20th century. However, given the booming construction industry and the increasing demand for housing, the demand for wallboard products has significantly exceeded the available manufactured supply of wallboard. This increased demand has dramatically driven the costs of wallboard products upward. Likewise, the need to supplement the natural gypsum wallboard products with the more costly synthetic gypsum products have also driven up the costs of wallboard products. These increasing cost factors have established a need for a lightweight, strengthened, and re-engineered wallboard product that minimizes the amount of gypsum present in the wallboard formulation.
Attempts have been made in the past to both strengthen and lighten traditional wallboard products, but such efforts have evidenced the addition of substantial costs to the finished product. For example, attempts have been made in the past to use a very low percentage of an inorganic or synthetic binder in wallboard formulations, typically 1% to 2%, in an effort to slightly effect the strength of the wallboard product. However, the amount of binder required to substantially increase strength and remain cost effective has not been realized. As disclosed herein and as a part of the present invention, it has been found that by placing the equipment needed to polymerize the base components of the synthetic binder on-site at the wallboard manufacturing facility, manufacturing costs may be greatly reduced.
Modern gypsum wallboard manufacturing facilities are very expensive in and of themselves, comprising numerous pieces of complex manufacturing and material handling equipment. Traditionally, the removal of the gypsum rock from gypsum mines or quarries is more difficult than strip or surface mining the softer Perlite ore from the mountain or ranges. After mining, the harder and larger gypsum rocks are crushed and reduced to smaller sizes and conveyed to where these smaller rocks are crushed into tiny particles. Next, the crushed gypsum is processed through a complex Calcining system involving a roller mill, a Calcining kettle, an imp mill and/or GC mill to reduce the gypsum fines into a chalk-like gypsum aqueous slurry. This Calcining system and process is expensive as it involves flash-drying and heating the gypsum land plaster or gypsum slurry in order to remove much of the water from the material. Following this dehydration process, the gypsum stucco is stored in holding bins and fed into equipment such as a pin mixer and a screw type conveyer. Water is again added along with other ingredients such as foams, starches, cementious materials and other chemicals to form the final prepared gypsum slurry. The gypsum paste is then spread onto and compressed between facing and backing paper and is cut further down the line. Next, a complex high temperature kiln dries the green gypsum board for approximately one hour or more, which is begun at lower temperatures (approximately 250.degree. F.), then to a higher temperature (approximately 600.degree. F.), and down again to exit from the kiln at lower temperatures (approximately 200.degree. F.), leaving the gypsum board virtually moisture-free. This complex system of processing and material handling equipment is extremely expensive, such that the start-up of a new facility to manufacture a new type of wallboard has in the past been cost prohibitive. It would therefore be advantageous to provide a means by which an existing manufacturing facility could be modified at little expense to produce a strengthened and lighter weight wallboard product.
Perlite and other minerals have previously been used in wallboard construction as a filler, and has likewise been used in a variety of other industrial uses, including abrasives, acoustical plaster and tile, charcoal barbecue base, cleanser base, concrete construction aggregates, filter aid, fertilizer extender, foundry ladle covering and sand additive, inert carrier, insulation board filler, loose-fill insulation, molding filler medium, packaging medium, paint texturizer, propagating cuttings for plants, refractory products, soil conditioner, tile mortar aggregate, and lightweight insulating concrete for roof-decks. Perlite is a glassy volcanic rock having the unusual characteristic of expanding to about 20 times its original volume when heated to an appropriate temperature within its softening range. The resultant expanded product finds a variety of industrial and constructional applications owing to the material's low density with attendant properties of low thermal conductivity and high sound absorption.
Petrographically, Perlite can be described as a glassy, volcanic, rhyolitic rock having a pearl-like luster and usually exhibiting numerous concentric cracks resembling an onionskin in appearance. Chemically, crude Perlite is essentially a metastable amorphous aluminum silicate. A typical average chemical analysis of Perlite would show a range of 71% to 75% SiO.sub.2, 12.5% to 18.0% Al.sub.2 O.sub.3, 4 to 5 percent K.sub.2 O, 1% to 4% sodium and calcium oxides, and minor amounts (traces) of metal oxides. Perlite is chemically inert and has a pH of approximately 7. The specific gravity of Perlite ranges from 2.2 to 2.4 (139 to 150 pounds per cubic foot) and has hardness between 5.5 and 7 (Mohs' scale). Crude Perlite may range from transparent light gray to glassy black in color; however, the color of Perlite when expanded will range from snowy white to grayish white.
Commercially, the term "Perlite" also includes the expanded product. When particles of Perlite are heated to a soft consistency, the combined water present (2% to 5%) in the glass vaporizes, forming steam that expands each particle into a mass of glass foam. The original volume of the crude Perlite may be expanded 4 to 20 times at temperatures between 1,200.degree. F. and 2,000.degree. F. Expanded Perlite may be a fluffy highly porous material or may be composed of glazed glassy particles having a low porosity. Dependent upon the inherent physical properties and processing variables, the bulk weight of expanded Perlite usually ranges from 2 to 20 pounds per cubic foot.
Specifications have been established by the American Society for Testing and Materials (ASTM) for the sizing and bulk density of expanded Perlite aggregate used for plaster and insulating concrete. Perlite for filter media uses and for many other uses usually follows specifications for proper sizing and other properties recommended by producers.
Perlite (expanded) can be graded by density in pounds per cubic foot, and classified by product number or trade name for producer and user identification. The expanded product can weigh as little as 2 pounds per cubic foot, but the most widely used bulk-density grade range is from 7 to 15 pounds per cubic foot. The range of expanded Perlite utilized in the wallboard composite core of the present invention is 4 to 10 pounds per cubic foot. Grades typical to this range include concrete, plaster, and cavity fill or masonry. The particle size ranges from 100 to 2,000 microns.
The expanded product is bagged for shipment and generally will be in volume of 4 cubic feet per bag. The expanded product is generally shipped via truck or rail. If by rail, the expanded product may be shipped in bulk dry density designed transport cars.
Expanded Perlite, depending on the expansion process and the grade of Perlite, can affect the expanded weight and can be used in the production of many products where weight is an important factor. In the construction industry, Perlite's incombustibility and low water absorption make it a superior insulating material. Perlite plaster aggregate is used extensively to fireproof structural steel construction and to reduce the weight of interior walls and ceilings. Perlite concrete aggregate roof-decks also insulate and save weight. Expanded Perlite is an important component of roof insulation (gypsum) board, masonry (cavity fill), and floor and wall tiles.
Some of the many important applications of Perlite include its use as an insulator (in cryogenic technology) to hold solidified gases such as liquid oxygen at extremely low temperatures, to absorb oil spills on water and wet surfaces, to clean up effluents containing oily wastes, and as an additive in molding sands.
In sum, while perlite has found a variety of uses in the construction industry, and even as a filler in wallboard products, it has not heretofore been effectively employed as a catalyst for significantly reducing the amount of gypsum required in the wallboard formulation.
Further, the green and/or gray-colored facing and backing paper used on standard gypsum wallboard is commonly low-grade and recycled, and performs poorly under rainy or wet surface conditions during shipping, construction, and the installation process. Weight factors of the gypsum drywall/sheetrock, as commonly termed, have been an ongoing concern during transportation and installation, as have general safety issues, particularly in hanging ceiling boards. Breakage and loss of material is an adverse factor during brittle gypsum board installation. It would therefore also be advantageous to provide an improved facing and backing paper lacking the shortcomings evident in the prior art.
3. Description of the Prior Art
The use of the main ingredient, calcium sulfate hemihydrate C.sub.A SO.sub.4.2H.sub.2 O, in the manufacture of gypsum wallboard and its related products has predominately been unchanged or unchallenged in its base components for over half a century. It has long been a conventional practice to finish the interiors and exteriors of buildings with gypsum core construction materials such as wallboard, lath, or sheathing. In general, these boards comprise essentially a core of set interlaced gypsum crystals disposed between fibrous, especially paper, liner sheets. After the gypsum slurry has set (i.e., reacted with the water from the aqueous slurry) and dried, the sheet is cut into standard wallboard sizes. Methods for the production of gypsum drywall are described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, 1970, Vol. 21, pages 621-24, the disclosure of which is hereby incorporate herein by reference.
It has been known to incorporate certain additional agents in the core of gypsum wallboard. These have included, for example, foam aggregate wherein a foam has been shredded to a rough consistency and then incorporated into the gypsum slurry prior to forming and setting thereof. Also, expanded mineral fillers such as perlite and/or vermiculite have been incorporated into the gypsum slurry in small amounts from 0.5 to 10 percent, in addition to organic adhesives such as starch or dextrin, or other fibers. Other agents have also been added, including simple chemicals which react within the gypsum slurry to form gasses. For example, carbonates are added to yield CO.sub.2 within the slurry; likewise, other air entraining agents, such as soap foams, may be employed to enable whipping air into the gypsum slurry during mixing.
Unfortunately, however, the amount of air or gas cells, or voids, which can be incorporated is limited, because the strength of the composite wallboard core is reduced when the amount of air cells is increased beyond a certain point. Likewise, the ability of the board to withstand a nail pull through the board is adversely effected by excessive air entraining. Additionally, historically expanded minerals were not added in gypsum wallboard beyond 2 to 3 percent because strength tests were significantly reduced, in both nail pull and flexural break tests, according to ASTM C79 and ASTM C473. While it has been an intention of individual inventors and major manufacturers to produce a lightweight, strengthened, and essentially improved wallboard product over current formulations, the problem of providing a wallboard product with increased strength while reducing its weight at a relative low cost has not been practically realized, either in re-engineering the wallboard itself or the manufacturing process thereof. Many combinations and compositions have been tried and tested in the past, but many remain unutilized due to impractical applications and/or significant increases in production costs. Reduced weight and density boards should meet or exceed industry standards and have strengths equal to or greater than their heavier counterparts according to ASTM standards. Such lightweight wallboard compositions should be able to be manufactured using conventional high-speed manufacturing apparatus and not suffer from other negative side effects of a completely different manufacturing process.
The addition of synthetic binders has very recently been attempted as disclosed in U.S. Pat. No. 5,879,825 to Burke et al.; however, the engineering and chemical research in various combinations of complex chemical formulations and combinations thereof has been quite limited. Additionally, the environmental concerns of noxious fumes under fire engineering standard ASTM testing E119 were not realized or considered, and cost considerations limited the amount of acrylic polymer to 1 to 2 percent, such that a polymer having a minimal cross-linking performance resulted. Further, while the use of Perlite as an antidessicant to prevent the dehydration of gypsum crystals formed during setting of the core composition is disclosed, no consideration is given to introducing an expanded mineral, such as perlite, as a substitute for gypsum as one of the structural foundations of the wallboard core, nor the specific need for a synthetic binder composition for establishing a complete crosslinking between the constituent elements of the wallboard core in order to create a molecular change within the strengthening agent, which molecular change is in turn required to completely bond a substantially reduced amount of gypsum with the other components of the wallboard core. Likewise, Burke et al. '825 discloses the use of its "strength-enhancing agent" only in the amount of 0.25 percent to about 2.5 percent solids, thus greatly limiting the cross-linking effect of the agent and the ability to significantly reduce the weight of the finished wallboard product.
Other attempts have been made in the prior art to provide adhesive compositions for use in bonding cellulosic and other porous materials. For example, U.S. Pat. No. 3,720,633 to Nickerson discloses a polyvinyl alcohol-based adhesive composition for use in paper converting applications. However, once again, no mention or suggestion is made of the need for a specific synthetic adhesive composition able to establish a sufficient cross-linking between its components to bind with gypsum and/or an expanded mineral to create a core material having the strength characteristics necessary to utilize the material as a wallboard sheet, while having a reduced weight over compositions that have been previously known.
Still further, U.S. Pat. No. 5,534,059 to Immordino, Jr. discloses a machinable plaster composition comprising a polymer-modified, gypsum based material, including a water redispersable powder polymer binder. However, in this instance, the polymer binder is used to produce a much more rigid, and thus easily machinable, plaster blank for use in conjunction with computer aided milling machines than previous compositions, and once again fails to disclose or suggest any combination which might be used to produce a strengthened yet lightweight wallboard having a synthetic binder which is fully cross-linking in order to establish a rigid bond with the gypsum and/or expanded mineral constituents of the wallboard core.
It would therefore by highly advantageous to provide a high strength, lightweight wallboard product which reduces the need for gypsum in the wallboard composition, and which utilizes a synthetic binder composition that enables a complete cross-linking of the constituent elements of the wallboard core to form a rigid structure with the structural integrity to withstand the structural requirements of traditional wallboard products. Such wallboard products should meet industry requirements, and likewise have a strength at least equal to previously known wallboard products while reducing the weight of the finished wallboard sheet. Such wallboard should also have the ability of being manufactured at existing, traditional gypsum wallboard production facilities without requiring such facilities to undergo a major renovation to undertake the new composition's production.
4. Summary of Invention
It has been discovered that a composition consisting essentially of a unique combination of synthetic binders selected for their ability to establish a permanent bond in the dry state, combined with an expanded mineral (e.g., Perlite and crushed Perlite), organic binding adhesives, drying agents, and hardeners, all contained within a covering of treated moisture and heat resistant paper material, produces an improved lighter-weight, strengthened wallboard product. The technology of the present invention utilizes an expanded mineral which physically becomes part of the composite matrix due to the complex formulation of binders attaching themselves to the mineral, instead of the mineral only acting as a filler. In comparison to the 1 to 10 percent of mineral filler previously utilized in gypsum wallboard, the expanded mineral can incorporate anywhere from 13 to 60 percent of the core composite of the present invention, thus dramatically decreasing the amount of gypsum required to makeup the core.
Numerous significant improvements have been made available through the improved wallboard of the present invention. First, the wallboard composition of the present invention enables a significant reduction of the amount of calcined gypsum required to produce the wallboard. This reduction in the amount of calcined gypsum stucco (through the use of perlite in the wallboard composition) in the method of the present invention expands the production capabilities of current wallboard manufacturing plants. Typically, the gypsum plants are limited in capacity production due to grinding of the gypsum ore or in calcination of the synthetic gypsum. Stretching the amount of gypsum required while reducing the energy and overall cost required greatly enhances the manufacturing production capabilities of the modified wallboard manufacturing facility of the instant invention.
More particularly, calcining equipment and gypsum supply have historically been the limiting factors in the production capacity in wallboard manufacturing facilities due to grinding limitations or calcine kettle limitations. Enlarged milling capacities become increasingly expensive as the gypsum calcining equipment is enlarged and/or improved in newer gypsum plant production. Typically, a standard wallboard manufacturing facility has one calcining operation supplying each wallboard production line. Additionally, the current domestic gypsum ore demand far exceeds the present supply; thus, the ability to spread the current gypsum ore supply and decrease the amount of gypsum grinding required in the present invention improves the production capacity of the wallboard manufacturing plant. Also, the present invention enables gypsum wallboard manufacturers to reduce the amount of calcined gypsum required to run a single boardline, and utilize their current single boardline gypsum supply to operate additional wallboard production lines, thus greatly increasing the production capacity of a given wallboard facility. As a result, the expense of purchasing additional expensive calcining milling equipment to increase production capacity is reduced.
A second benefit of the lightweight technology of the present invention allows for a wallboard composition that is significantly lighter in weight (up to fifty percent lighter) than current traditional heavy gypsum wallboard formulations. This reduced weight also results in transporting lighter loads, in turn reducing transportation costs. Further, job site labor costs are reduced by enabling the workers to handle lightened loads, such that the installation process is made easier and less costly. Similarly, the potential for heavy wallboard related injury accidents to the tradesmen that install the wallboard are reduced.
Yet another benefit of the strengthened wallboard of the instant invention is the reduction in the amount of board breakage and losses due to manual or machine transport to the installation site, due to the fact that the composition of the instant invention provides the wallboard with greater flexibility than has been known in previous wallboard compositions.
Still further, the wallboard composition of the instant invention exhibits equal or greater strength than current heavy gypsum wallboard, with improvements in moisture resistance and flame resistance that exceeds current industry standards. This lightweight and strength factor equates to decreased structural support load bearing and lessens the total support strength required in any project, in turn further reducing overall construction costs.
The specific constituents of the wallboard core (as set forth in detail below) have been found to improve upon the overall structural strength of the wallboard, lighten its weight, decrease the amount of airborne particulates during breakage, decrease its brittleness, and expand its flexibility. Further, the high quality wallboard composition of the present invention is completely cost effective to manufacture using typical existing wallboard manufacturing equipment and practices with limited minor modifications and additional equipment, as further described herein.
The attempted addition of synthetic binders in the past to wallboard compositions have reduced the ability to cut the finished wallboard sheet during installation with a utility knife. However, the composition of the instant invention was developed after several hundred tests and analysis of numerous chemical combinations, with extensive chemical technical research and testing to realize a brittle cross-linking complex polymer that combines and fuses with the mineral and expanded mineral, that is easily cut and snapped with a utility knife as applied in standard construction industry use. Further, there has not previously been available a lightweight, strengthened, and re-engineered wallboard product formulated with minor low cost changes in the manufacturing process that is environmentally friendly and cost effective to produce.
Optionally, reinforcing fibers, fire retardants, water repellents, and other water proofing materials may be part of the composition. Further, the technology of the present invention allows for decreased set times from the pin mixer to the knife in laboratory testing, which in turn increases boardline manufacturing speeds far beyond what is currently being realized. As manufacturing speeds increase, so does production, enabling greater amounts of wallboard to be produced to meet the current demand. This complex formulation of binders can be seen to be utilized in a wide variety of other building materials as well.
The paper covering or veneer of traditional gypsum wallboard consists of wastepaper constituents that include, but are not limited to, waste newspapers, old corrugated papers, kraft cuttings, and flyleaf shavings. As a result, there are wide variants in wallboard covering coloration which include brown, tan, grey, pink green and grey-white colors. Additionally, traditional gypsum wallboard strength is largely dependent on the strength of the covering paper, as evidenced by the dependence of the results of the flexural break strength and nail pull resistance tests (according to ASTM C-473) on paper fiber strength. Optionally, the present invention provides increasing break strength of the paper covering sheets by increasing fiber length and/or by altering the top ply by utilizing a paper laminate which provides consistent off-white colorization.
The improved, strengthened core material of the instant invention also provides increased compression, shear, and tension loading test results in comparison with the conventional non-reinforced gypsum drywall. ASTM Test Standard C79 standard specifications for gypsum sheathing board require that specimens shall surpass an average surface water absorption of not more than 1.6 g after 2 hours of elapsed time (Section 5.1.7). While gypsum wallboard is required to meet the above ASTM standards, moisture resistance and adverse weather conditions have been long-term problems with gypsum drywall. The improved wallboard of the instant invention comprises an improved moisture resistant cover and core material that far surpasses ASTM C79-5.1.7. Thus, the present invention improves the structural strength, moisture resistance, and weight factors in the design of a new wallboard or ceiling board to be utilized as a construction material, whereby gypsum is not the primary core ingredient.
A preferred embodiment of the invention is further directed to a method for producing expanded Perlite wallboards of a thickness not less than 1/4 inch and not greater than 1 inch comprising the steps of: adding starch, boric acid, foamer, gypsum, and a latex vinyl acetate emulsion with water to expanded Perlite to form a composition; the aqueous slurry of settable Perlite is enveloped between two high quality paper cover sheets comprised of recycled virgin pulp and formed into a board; directing the continuous board away from the forming apparatus to a cutting knife where it is cut to desired length; and finally drying the board in a high temperature kiln at temperatures ranging from 75.degree. C. to 325.degree. C. Optionally, the process further includes the steps of forcing hot air to an encapsulated section of board line, starting the curing process prior to the board reaching the board cutting knife.
As previously mentioned, gypsum board manufacturing is a complex process from the collection of the gypsum rock to the production of the completed wallboard. However, the improved wallboard product of the instant invention, as described more fully in the examples below, offers increased wallboard production capacity from a given gypsum supply over traditional gypsum wallboard products and methods of manufacture. Optionally, when gypsum is not utilized in the wallboard core, the entire calcining system is eliminated from the manufacturing process, and curing temperatures in the manufacturing are substantially reduced. This also greatly reduces the overall production cost of the improved wallboard of the instant invention.
Yet another improvement of the improved wallboard product of the present invention comprises the environmental improvements resulting from a reduction of the half-life of the breakdown of the wallboard core material. Perlite is a more inert material than gypsum. Thus, it is safer to the environment because it does not react with or leach into ground water. Further, the adhesives used in the wallboard product of the instant invention decompose very quickly and easily. Thus, the improved wallboard of the present invention provides a lightweight, strengthened, fire retardant, whitish-covered Perlite wallboard with environmental improvements that is competitively priced to traditional gypsum wallboard products.